The present invention relates to a heat dissipating material and a method for manufacturing the material. More particularly, the present invention pertains to a heat dissipating material suitable for heat dissipating substrate, on which electronic components such as semiconductor devices are mounted.
Since electronic components such as semiconductor devices produce heat during operation, such components need to be cooled so that the performance will not lowered. Accordingly, methods for implementing semiconductor devices on a heat dissipating board (heat dissipating substrate) have been proposed. These methods include a method using a heat sink and a method using a heat spreader.
A heat sink using method is shown in FIG. 4. A heat sink 42 is fixed to an aluminum base 41, which forms a case, with screws (not shown). The heat sink 42 may be soldered to the aluminum base 41. An insulated substrate 43 is fixed to the heat sink 42. The insulated substrate 43 has metal (Al) layer 43a on each side. An electronic component 44 such as a semiconductor device is implemented onto the upper metal layer 43a of the insulated substrate 43. The insulated substrate 43 is made of aluminum nitride (AlN). The heat sink 42 is made of a material having a low expansion coefficient and a high thermal conductivity. Specifically, the heat sink 42 is made of metal matrix composite, which has ceramics dispersed in a metal matrix layer. For example, a composite having SiC particles dispersed in an aluminum main component is used.
Aluminum nitride of the insulated substrate 43 and the metal matrix composite of the heat sink 42 are expensive. Therefore, an inexpensive method using a heat spreader has also been proposed.
A heat spreader using method is shown in FIG. 5. A high insulated thermal technology (HITT) substrate 45 is secured to the upper surface of an aluminum base 41, which forms a case, with silicone grease. The HITT substrate 45 includes an aluminum main body 45a, an epoxy resin insulating layer 45b, and a metal (copper) layer 45c. The insulating layer 45b is adhered to an opposite side of the main body 45a from the aluminum base 41. The metal layer 45c is laminated on the insulating layer 45b. A heat spreader 46 is soldered onto the HITT substrate 45. An electronic component 44 is soldered onto the heat spreader 46. Currently, heat spreaders are made of Cu, Mo or a three-layer laminated material of Cu/Invar/Cu. Invar is an alloy containing 36% of weight of Ni. The remaining portion of Invar is substantially Fe.
However, Cu has a relatively great linear expansion coefficient of 17xc3x9710xe2x88x926/xc2x0 C. Therefore, matching between Cu and the electronic component 44, the linear expansion coefficient of which is 4xc3x9710xe2x88x926/xc2x0 C., is not satisfactory. Also, since Mo has a relatively low linear expansion coefficient of 4xc3x9710xe2x88x926/xc2x0 C. to 5xc3x9710xe2x88x926/xc2x0 C., matching between Mo and the HITT substrate 45 is not satisfactory.
On the other hand, the three-layer laminated material of Cu/Invar/Cu, which is used nowadays, has a linear expansion coefficient of 10xc3x9710xe2x88x926/xc2x0 C. to 11xc3x9710xe2x88x926/xc2x0 C. Thus, the laminated material has satisfactory matching with the electronic component 44 and the HITT substrate 45. However, Invar contained in the laminated material has a significantly small thermal conductivity. Thus, although Invar is held between Cu layers having a relatively high thermal conductivity (390W/(mxc2x7K)), the heat expansion of the heat spreader 46 in the direction of thickness is as small as 30W/(mxc2x7K). As a result, if considered as a uniform material, the heat conductivity of the three-layer laminated material is as small as 60W/(mxc2x7K), which is not sufficient for dissipating heat. Further, since Invar is held between Cu layers, the cost is increased.
Accordingly, it is an objective of the present invention to provide an inexpensive heat dissipating material that can be used as a heat spreader.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a plate-shaped heat dissipating material is provided. The main component of the material is an iron-based metal, and at least the surface of the material is covered with a rustproof metal.
The present also provides an electronic module including a plate shaped heat dissipating material and an electronic element. The main component of the material is an iron-based metal, and at least the surface of the material is covered with a rustproof metal. The electronic element is mounted on the heat dissipating material.
The present invention further provides a method for manufacturing a heat dissipating material. The method includes: placing metal shaving in a mold; pouring a molten aluminum-based metal or molten copper into the mold and impregnating the metal shaving with the molten aluminum-based metal or the molten copper; and taking out the molded material as the heat dissipating material from the mold after the aluminum-based metal or the copper is solidified.
The present invention provides another method for manufacturing a heat dissipating material. The method includes: forming a porous sintered compact with powder of an iron-based metal; placing the sintered compact in a mold; pouring and pressurizing a molten aluminum-based metal or molten copper into the mold, and impregnating the sintered compact with the molten aluminum-based metal or the molten copper; and taking out the molded material as the heat dissipating material from the mold after the aluminum-based metal or the copper is solidified.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.